The desirability of obtaining equal torque output from each cylinder of a multi-cylinder internal combustion engine has long been recognized. For this purpose it has recently been proposed, as disclosed, for example, in the SAE Publication 820207 entitled Digital Analyzer for Internal Combustion Engines by C. K. Leung and J. J. Schira, or, as disclosed in Research Disclosure No. 18002 published in Research Disclosure, April 1979, to use engine cylinder variation to control cylinder-to-cylinder fuel distribution so as to obtain substantially equal torque contributions from each cylinder in a multi-cylinder engine.
As disclosed in these publications, for diesel engines and spark ignition engines with A/F ratios greater than 13.8, a slight increase in fuel supplied to a cylinder will increase the torque produced by that cylinder. Accordingly, the output of each cylinder is compared with the average output of all cylinders to determine the amount of correction needed for each cylinder. As an example, for this purpose engine speed variations between the individual cylinders are measured because the relative magnitudes of the individual cylinder outputs can be obtained by measuring the cylinder-to-cylinder amplitude variation of the speed variation signal. These signals are then used, as in an electronic fuel injection system of the type with an onboard computer, to control fuel flow to the respective cylinder in a manner to provide substantial equal torque output among the cylinders.